Growth performance and feed utilization
Shrimp fed with spirulina-supplemented diets exhibited significantly improved growth performance compared to the control group, as shown in Table 3. Final weight ranged from 8.21±0.15 g (control) to 10.82±0.08 g (Treatment 2), with Treatment 2 showing significantly higher growth parameters than all other treatments (
p<0.05; Tukey’s HSD post hoc test applied). Weight gain, specific growth rate (SGR) and protein efficiency ratio (PER) were also highest in Treatment 2, indicating superior feed utilization efficiency. The feed conversion ratio (FCR) was most efficient in Treatment 2 (1.61±0.01), significantly lower than the control (
p<0.05). Survival rates across all groups were high (95.02%-98.51%) with no significant differences (
p>0.05). These results suggest that spirulina inclusion up to 10% enhances shrimp growth while maintaining survival, potentially through improved nutrient utilization and feed efficiency.
Proximate analysis shrimp body
Dietary spirulina supplementation significantly improved the nutritional composition of
P. vannamei, as shown in Table 4. Shrimp in Treatment 2 (10% spirulina) exhibited the highest dry matter (24.34±0.23%) and crude protein (23.51±0.45%) contents, both significantly higher than the control and other treatments (
p<0.05; Tukey’s HSD). Crude fat content was also significantly higher in Treatment 2 (9.88±0.32%), followed by Treatment 1. The highest ash content (2.73±0.85%) was observed in Treatment 3, suggesting potential mineral retention at higher spirulina inclusion. Moisture content (74.32%-75.45%) showed no significant differences across treatments (
p>0.05). These findings indicate that spirulina improves protein and lipid deposition in shrimp muscle, potentially enhancing flesh quality and energy storage, which are important for growth and immunity.
Water quality parameter
Water quality parameters remained within optimal ranges for
P. vannamei throughout the experiment, as shown in Table 5. Temperature (28.10-28.22
oC) and salinity (31.9-32.2 ppt) showed no significant differences (p>0.05). However, dissolved oxygen and pH were significantly higher in Treatment 2 (5.41±0.12 mg/L and 7.82±0.27, respectively) compared to the control (p<0.05), likely due to enhanced microbial activity from spirulina supplementation. Ammonia, nitrate and nitrite levels were significantly lower in spirulina-fed groups, with Treatment 2 showing the lowest values, indicating improved water quality and nitrogen utilization (p<0.05).
Immune parameters
Total haemocyte count
On Day 1, total haemocyte count (THC) values were uniformly low across all groups (EC, PC, T1, T2, T3), with no statistically significant differences (
p>0.05), indicating a baseline immune status at the start of the experiment (Fig 1). By Day 3, a significant increase in THC was observed across all groups, with the highest counts recorded in Treatment 1 (T1) and Treatment 2 (T2). The THC values in these groups were significantly higher compared to both Day 1 and Day 5 (
p< 0.05), suggesting a marked immune activation in response to spirulina supplementation. By Day 5, THC values declined from the Day 3 peak but remained significantly elevated compared to Day 1 (
p<0.05). At this point, no significant differences were detected among the treatment groups, indicating a potential return to immune equilibrium.
Respiratory burst activity
Respiratory burst activity showed no significant differences among groups on Day 1 (
p>0.05), suggesting similar baseline oxidative responses across treatments. By Day 3, a significant reduction in respiratory burst activity was observed in all groups compared to Day 1 and Day 5 (
p<0.05). This reduction may reflect a temporary suppression of respiratory burst mechanisms following initial immune stimulation. By Day 5, respiratory burst activity increased again and returned to levels comparable to Day 1, indicating recovery or normalization of immune function, as shown in Fig 2.
Prophenoloxidase activity
Prophenoloxidase activity was initially high in all groups on Day 1, with no significant differences among treatments (
p>0.05). By Day 3, a significant decline in activity was noted across all groups (
p<0.05), though levels remained higher than those observed on Day 5. On Day 5, ProPO activity further decreased significantly to its lowest point (
p<0.05). A significant interaction between treatment groups and sampling days was observed, indicating that the decline in ProPO activity was influenced by both treatment and time. These results suggest that ProPO activity undergoes a time-dependent reduction post-stimulation, possibly due to regulatory immune feedback mechanisms (Fig 3).
Superoxide dismutase (SOD) activity
Superoxide dismutase activity was lowest on Day 1 across all groups (
p>0.05), indicating a baseline antioxidant status, as shown in Fig 4. By Day 3, SOD activity significantly increased in all groups, with Treatment 2 exhibiting the highest activity (
p<0.05), suggesting an upregulation of antioxidant defences in response to spirulina supplementation. This trend continued on Day 5, where SOD activity remained significantly elevated, particularly in Treatment 2, demonstrating a sustained antioxidant response that may contribute to improved immune resilience.
Catalase (CAT) activity
Catalase activity was highest across all groups on Day 1 (
p<0.05), indicating an immediate oxidative stress response, as shown in Fig 5. By Day 3 and Day 5, CAT activity significantly decreased in all groups (
p<0.05), with no significant differences among treatments at these later time points. The observed decline suggests a time-dependent reduction in oxidative stress, possibly reflecting physiological adaptation or effective antioxidant regulation induced by spirulina supplementation.
Cumulative mortality
Following
V. parahaemolyticus challenge, the pathogen control (PC) group exhibited the highest cumulative mortality (50%). In contrast, shrimp fed spirulina-supplemented diets showed reduced mortality: 40% in Treatment 1 and 30% in both Treatment 2 and Treatment 3, with mortality stabilizing in Treatment 3 after Day 9. No mortality was observed in the unchallenged experimental control (EC). These findings suggest that dietary
S. platensis, particularly at higher inclusion levels, enhances disease resistance and improves survival outcomes in
P. vannamei as shown in Fig 6.
Growth performance
The present study investigated the effects of dietary
S. platensis supplementation at 0%, 5%, 10% and 15% inclusion levels on the growth performance and survival of
P.vannamei. The results revealed that the 10% inclusion level (T2) significantly improved final weight, weight gain, specific growth rate (SGR) and protein efficiency ratio (PER), while reducing feed conversion ratio (FCR), indicating optimal utilization of nutrients. The findings are consistent with the research conducted by
Teimouri et al., (2013), which indicated that replacing fish meal with up to 10%
Spirulina platensis (SP) significantly enhances the growth performance of rainbow trout. Similarly, replacing fishmeal with 10%
S. platensis meal in
Lates calcarifer diets improved growth, feed efficiency, gut enzyme activity and immune-antioxidant responses. The 10% inclusion is recommended for better performance and health in juveniles
(Mousavi et al., 2025).
Li et al., (2022) observed that the inclusion of dried algae as a feed supplement significantly enhanced feed intake (FI), improved feed conversion ratio (FCR), elevated carcass quality and supported better growth metrics. moreover, it contributed to an improved physiological condition during adverse circumstances, such as stress and disease. SP is high in Polyunsaturated fatty acids (PUFA), especially the n-3 and n-6 varieties that are essential for the synthesis of biomembranes (
ViglianoRelva et al., 2024). These blue-green microalgae improve the intestinal flora of shrimp by breaking down indigestible feed components and increasing the production of enzymes that assist in fat metabolism (
Jaime-Ceballos et al., 2006;
Sandeep et al., 2023). SP enhances growth and feed efficiency by increasing the population of beneficial bacteria in the gastrointestinal tract (
Jaime-Ceballos et al., 2006). Likewise, in the present study, spirulina-fed shrimp showed better growth performance than the control.
Moreover, the survival rate was highest in the T2 group, suggesting that Spirulina may contribute to immune enhancement. Studies have demonstrated that Spirulina exerts immunomodulatory effects by stimulating phagocytic activity and enhancing resistance to bacterial infections such as vibriosis (
Al-Ghanayem, 2023). In the present study, a 15% inclusion level (T3) showed improvements over the control group but did not exceed the performance of the 10% group. This suggests a plateau effect at higher inclusion levels, supported by earlier studies indicating that excessive dietary Spirulina may negatively impact palatability or nutrient balance
(Li et al., 2022).
Whole body proximate composition
Dietary inclusion of
S. platensis significantly influenced the proximate composition of
P. vannamei. In the present study, a 10% inclusion level (T2) produced the highest protein (23.51± 0.45%) and fat (9.88±0.32%) contents. The results are consistent with the earlier research conducted by
Hossain et al., (2017) and
Sukri et al., (2016). The increased ash content in the 15% group (2.73±0.85%) may be attributed to Spirulina rich mineral composition, which includes calcium, magnesium and iron, essential for shrimp growth and metabolism
(Abdelnour et al., 2020). Moisture levels remained consistent across treatments, indicating no adverse effect of Spirulina on tissue hydration. These results are consistent with earlier findings that Spirulina improves body composition and feed quality in aquatic species when included at optimal levels
(Wang et al., 2025).
Immune response
This study evaluated the immunomodulatory effects of dietary
S. platensis at varying inclusion levels (5%, 10% and 15%) in
P. vannamei over a 60-day feeding period, followed by a pathogenic challenge with
V. parahaemolyticus. The results of the current study showed that the incorporation of dietary dried
S. platensis supplements significantly enhanced resistance to the pathogenic bacteria
V. parahaemolyticus.
P. vannamei fed with Spirulina-supplemented diets (T1, T2, T3) demonstrated a significant enhancement in total hemocyte count (THC), particularly on Day 3, when compared to the control groups (EC and PC), indicating a strengthened cellular immune response. Respiratory burst activity, which is essential for the production of reactive oxygen species involved in pathogen elimination, was also significantly higher in Spirulina-fed groups, especially on Days 3 and 5. Additionally, prophenoloxidase (PO) activity, a key component of the shrimp immune defense, was elevated on Day 1 in the Spirulina-fed groups and remained consistently higher than the control groups throughout the study period. Superoxide dismutase (SOD) activity, which plays a critical role in antioxidant defense, was also significantly upregulated in shrimp receiving Spirulina, suggesting improved management of oxidative stress during pathogenic challenges. These results align with the findings of
Tayag et al., (2010), who reported that hot-water extracts of
S. platensis enhanced innate immunity in
P. vannamei, as evidenced by increased hemocyte counts, immune enzyme activities and resistance to
V. alginolyticus following both injection and immersion treatments. Similarly,
Chen et al., (2016) demonstrated that dietary supplementation with dried Spirulina powder significantly boosted lysozyme activity and improved shrimp resistance to
V. alginolyticus infections, further supporting Spirulina role as an effective immunostimulant in shrimp aquaculture.
Overall, the results of this study demonstrate that dietary Spirulina, particularly at 10% inclusion (T2), can effectively enhance both antioxidant and immune responses in
P. vannamei, thereby improving resilience against
V. parahaemolyticus infection.